Printhead

ABSTRACT

A printhead comprising: a housing having an inlet for the supply of ink; an array of ejection locations for the ejection of ink droplets; an ink supply pathway for the passage of ink from the inlets to the ejection locations, wherein the ink supply pathway comprises at least one divergent ink manifold; and an outlet manifold for receiving ink from the ejection locations.

The present invention relates to a printhead. More particularly, themethod and apparatus employed may be generally of the type described inWO-A-93/11866, the disclosure of which is incorporated herein byreference. In the above patent specification, an agglomeration orconcentration of particles is achieved in the printhead and, at theejection location, the agglomeration of particles is then ejected on toa substrate, e.g. for printing purposes. In the case of an arrayprinter, plural cells may be arranged in one or more rows.

It is well known to generate and eject particles by use of electrostaticfields from a plurality of ejection locations wherein each of theejection locations is supplied with ink. It is important that the inkreaches each ejection location in the array under the same conditionsi.e. no location is without ink when others have been supplied, and inthe same condition, such as temperature, pressure and concentration.This ensures that the composition of the ink used during printing isidentical at each ejection location and that locations which mayotherwise be at one of the extremes of an array, and thereforesusceptible to not receiving an adequate supply of ink, are suppliedwith the same amount of ink under the same conditions as the ejectionlocations at the centre of the array.

Furthermore, when an intermediate electrode is provided surrounding thearray of ejection locations, it is imperative that the intermediateelectrode can be quickly and accurately positioned in such a manner thatdoes not increase the risk of damage occurring to the ejection locationwhich it surrounds. Clearly, damage of any of the ejection locations isundesirable as it will affect the quality and accuracy of any printingwhich is carried out by the printhead.

Therefore, it is the aim of the present invention to provide a printheadwhich overcomes the problems identified above.

According to the present invention, there is provided a printheadcomprising:

-   -   a housing having an inlet for the supply of ink;    -   an array of ejection locations for the ejection of ink droplets;    -   an ink supply pathway for the passage of ink from the inlet to        the ejection locations, wherein the ink supply pathway comprises        at least one divergent ink manifold, and    -   an outlet manifold for receiving ink from the ejection        locations.

Preferably, the manifold is divergent in the direction from the inlet tothe outlet.

Preferably, the manifold includes at least one inlet and one outlet forthe passage of ink, the outlet supplying ink to the array of ejectionlocations.

The manifold is preferably symmetrical about a line normal to and in thecentre of the array of ejection locations.

The manifold may take the form of a triangular passageway and the inletmay be provided at an apex of the manifold and the outlet(s) is (are) onthe side of the manifold opposite the inlet.

Alternatively, the manifold may take the form of a substantially semicircular chamber, with the outlet(s) from the chamber being located onthe substantially straight boundary of the manifold. The manifold mayalso take the form of a particularly elliptical or parabolic chamber.Preferably, the inlet is therefore located at the focus of the shape ofthe manifold.

In the arrangement whereby the array of ejection locations is very wide,it is envisaged that a plurality of ink supply manifolds could beprovided such that each supplies a substantially equal portion of thearray. The inlets to each of the manifolds may be supplied by a commonmanifold of the type previously described, such that the ink which issupplied to the ejection locations is still under the same conditionsacross the entire array, as it has initially been supplied through asingle inlet to the first pathway.

The printhead may further be provided with a fluid flow layer in which aplurality of fluid passageways are provided and through which a gas or aliquid, such as a rinse agent, can be caused to flow. Such flow can beutilised to clean the channels or to clean the intermediate electrode.

The outlet manifold may have the same form as the inlet manifold or maybe a different shape. Preferably the outlet manifold is convergent fromits inlet towards its outlet. The shape of the outlet manifold isimportant in ensuring that the negative pressure applied to theprinthead is uniform and that all of the ink is recirculated, such thatno pockets of static ink are created.

The cross sectional area of the manifold(s) may be kept constant, suchthat as the width increases, the thickness is reduced.

The manifolds may be provided with a plurality of ink inlets or mayalternatively be provided with a single inlet. The outlet manifold ispreferably provided with a single outlet for returning the ink to a bulkink supply.

It is preferable that the upper edges when in use, of the manifolds, arecurved so that any air bubbles that are present are caused to float tothe top of the manifold. The manifold is preferably provided with one ormore air bleed outlets for the removal of air bubbles. It is preferablethat an air bleed is located at the apex of a manifold.

One or both of the manifolds may be provided with one or more supportstructures to maintain the required thickness of the manifold.

A second aspect of the present invention provides a printheadcomprising:

-   -   a housing;    -   an array of ejection locations for dispensing ink droplets; and    -   an intermediate electrode surrounding the array of ejection        locations;    -   wherein the intermediate electrode is removably connected to the        housing.

Preferably the intermediate electrode is connected by means of akinematic mount.

The printhead may also include one or more magnets mounted on one of thehousing or the intermediate electrode for attracting the other of thehousing and the intermediate electrode.

The kinematic mount comprises recesses on either the printhead or theintermediate electrode, one of which is conical, one of which isV-shaped, and one of which has a flat bottom. The other of the printheadand intermediate electrode is preferably provided with ball bearingswhich, when the intermediate electrode is mounted to the housing, arelocated within the corresponding recesses.

Additional magnets may be provided on one or both of the housing and theintermediate electrode.

The contact inserts of the kinematic mount may be electricallyconductive to provide an electrical contact to the intermediateelectrode. The inserts may be gold plated.

A third aspect of the present invention provides a printhead comprising:

-   -   a housing;    -   an array of ejection locations for dispensing ink droplets;    -   an intermediate electrode surrounding the array of ejection        electrodes; and    -   a fluid flow layer having at least one passageway through which,        in use, a fluid can be caused to flow, the fluid being directed        towards one or both of the array of ejection locations or to the        intermediate electrode.

The fluid may be a gas, such as air or may additionally or alternativelybe a liquid, such as a rinse agent or a solvent In both cases, the fluidflow causes ink deposits to be removed from either the ejectionlocations or from the intermediate electrode.

A fourth aspect of the present invention includes a method of cleaning aprinthead, the printhead having a housing, an array of ejectionlocations for dispensing droplets and an intermediate electrodesurrounding the array of ejection locations, the method comprising thesteps of:

-   -   supplying pressurised cleaning fluid to a fluidic network within        the housing;    -   directing the pressurised cleaning fluid towards one or both of        the array of ejection locations and the intermediate electrode.

Preferably, the cleaning fluid includes one of compressed gas and aliquid which are preferably air and a rinse agent respectively.Preferably, the cleaning fluid is collected after cleaning, is filteredand can therefore be reused.

One example of the present invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a printhead according to the presentinvention;

FIG. 2 shows a perspective view from the other side of the printheadwith the intermediate electrode removed;

FIG. 3 shows the intermediate electrode;

FIG. 4 is a schematic cross sectional view through the ejection portionof the printhead;

FIG. 5 a in an exploded view of an ink inlet structure;

FIG. 5 b is an exploded view of an ink outlet structure;

FIG. 6 a is a perspective view of the ink inlet structure;

FIG. 6 b is a detailed view of part of the ink inlet structure;

FIG. 6 c is a perspective view of the ink outlet structure;

FIG. 6 d is a detailed view of part of the ink outlet structure;

FIG. 7 is a schematic plan view of one example of a manifold;

FIG. 8 is a schematic plan view of an outflow manifold;

FIG. 9 is a schematic plan view of one example of an inflow manifold;and

FIG. 10 is a schematic view of a maintenance system for use in theprinthead.

The printhead 1 shown in FIG. 1 comprises a main body 2 to which theremaining components are connected. On one end of the main body, anintermediate electrode plate 3 is mounted by means of a kinematic mount(see FIGS. 2 and 3). The main body 2 is connected to a mounting portion4, comprising a location plate 5 and a fixed plate 6 held together bymeans of thumb screws 7 which pass through a wavy washer 7 a.

The main body 2 comprises a substantially level base portion 8 and apair of upstanding projections 9, to which the intermediate electrodeplate 3 is mounted.

As shown in FIG. 2, the kinematic insert comprises three recesses 10,11, 12 on the main body and these include one flat bottomed recess 10,one V-shaped recess 11 and one conical recess 12. Magnets 13 areinserted in the surface of the main body.

The intermediate electrode plate 3 comprises a datum plate 14 to whichball bearings 15 and additional magnets 16 are fixed and theintermediate electrode 17 itself, which is mounted in an opening in thedatum plate. Openings 71 are provided in the datum plate 14 to receivecorresponding projections 70 on the housing 2. The projections could, ofcourse, be located on the datum plate and the openings on the housing.

The flat portion 8 of the main body 2 supports a laminate structure 18,shown in FIG. 4, which includes a fluid flow layer 19, an ink outletmanifold 20, an ink outlet layer 21, a central tile 22, an ink inletprism 23, an ink inlet manifold 24, an air bleed outlet 25 and an inkinlet layer 26, as can be seen in FIG. 4.

The central tile 22 includes channels (not shown) for supplying ink toan array of ejection locations 27.

The laminate structure 18 is held in place by an upper part 28 of theprinthead which acts as a clamp and is held in place by means of a plate29 which is fixed to the main body by means of screws 30.

The ejection locations 27 are controlled by means of electrical signalssupplied via electrical connectors 31 which are mounted on rigid plates32. The electrical connectors are each connected to a flexible sheet 33which has individual electrical pathways corresponding to each ejectionlocation, and these are connected to the individual channels in thecentral tile 22.

The fluid flow layer 19 shown in FIG. 4 include a series of narrowchannels 34, shown in FIGS. 6 c and 6 d, through which a gas or aliquid, such as a rinse agent, can be caused to flow. Whilst only asingle fluid flow layer is shown, it is envisaged that additional fluidflow layers could be included. This is discussed in greater detail withreference to FIG. 10.

The ink is supplied by means of ink supply tubes 35 in the printheadwhich feed ink through the ink inlet layer 26 and the air bleed layer25, into the ink inlet manifold 24, examples of which can be seen inFIG. 7 and 9. The ink passes through chamber 37 in the manifold 24 andexits, through the ink inlet prism 23 to the ejection locations 27 onthe central tile 22. The ink then flows from the central tile 22 throughthe ink outlet layer 21 into the ink outlet manifold 20, one example ofwhich can be seen in FIG. 8. The ink leaves the ink outlet manifold andpasses back into the bulk ink supply (not shown).

As can be seen in FIGS. 5 a, 5 b and 6 a to d, the ink inlet prism 23comprises a series of narrow channels 60, corresponding to each of theindividual ejection locations 27 in the central tile 22. The ink passesalong the channels 60 and enters the ejections locations 27. The outletmanifold 20 in FIG. 5 b includes a triangular chamber 42, but thischamber may be the same shape as chamber 37 in the inlet manifold 24 ormay be shaped as shown in FIG. 8.

FIG. 7 shows a schematic plan view of one example of an inlet manifold24. The manifold is provided with an inlet 36 from the bulk ink supplywhich feeds into a manifold chamber 37. The chamber includes a number ofsupports 38 to maintain the required thickness of the chamber and, also,to direct the ink flow in the required directions.

FIG. 8 shows one example of an outlet manifold 20, in which the inkenters a manifold chamber 42 along the straight boundary 39 and passesthrough and exits via an ink outlet. Again, a number of supports 41 areprovided to maintain the required thickness of the outflow manifoldchamber. The supports 38 and 41 are optional.

FIG. 9 shows another example of an inlet manifold 24, in which a numberof ink inlets 43 are provided, together with a number of supportstructures 44. An air bleed outlet 45 is also provided to remove airbubbles which may be entrained in the inlet ink flow and which areundesirable.

FIG. 10 shows the main features of a maintenance system 50 which couldbe used in the printhead shown in the earlier Figures. The maintenancesystem includes a rinse reservoir 51 supplying a liquid to a pump 52which delivers the flow via a valve 53 into a supply line 54 to theprinthead 1. Also connected to this supply line via a further valve is acompressed air supply line 55. In this way, either liquid or air, or acombination, can be supplied through the channels 34 (not shown) in theink flow path of the central tile 22 or the channels 34 of the fluidflow layer 19 shown in FIG. 5. The flow path includes the two manifoldsand the ejection locations. The compressed air supplied via the airline55 provides additional agitation in the flow, thereby improving thecleaning action of the fluid as it passes along the ink supply path. Itis envisaged that the liquid and the gas may be supplied at the sametime, or as separate flow streams, one after the other. The addition ofthe compressed air into the fluid also provides additional agitation atthe printhead 1. By switching off this stream of air, fluid can bepumped into both sides of the printhead, leaving it fully primed.Additional valves (not shown) are provided to allow a user to switchbetween maintenance and printing configurations. The used clean fluidpasses through a filter 56 into a filtered rinse collection reservoir 56for recirculation back to the pump 52.

The maintenance system can be utilised to clean the ejection locations27 or the intermediate electrode 17 or both. When cleaning the ejectionelectrodes, it is preferred that both rinse agent and compressed air areused.

When cleaning the intermediate electrode 17, the fluid flow, includingcompressed gas, acts as a gas brush.

Additional fluid outlets, directing fluid to other parts of theprinthead, may be provided.

1. A printhead comprising: a housing having an inlet for the supply ofink; an array of ejection locations for the ejection of ink droplets; anink supply pathway for the passage of ink from the inlets to theejection locations, wherein the ink supply pathway comprises at leastone divergent ink manifold; and an outlet manifold for receiving inkfrom the ejection locations during printing.
 2. A printhead according toclaim 1, wherein the manifold includes at least one inlet and at leastone outlet for the passage of ink, the outlet supplying ink to the arrayof ejection locations.
 3. A printhead according to claim 2, wherein themanifold is divergent in the direction from the inlet to the outlet. 4.A printhead according to claim 1, wherein the manifold is symmetricalabout a line normal to and in the centre of the array of ejectionlocations.
 5. A printhead according to claim 1, wherein the manifold isa triangular passageway.
 6. A printhead according to claim 5, whereinthe inlet is provided at an apex of the manifold and the outlet(s) is(are) on the side of the manifold opposite the inlet.
 7. A printheadaccording to claim 5, further comprising an air bleed outlet at an apexof the manifold.
 8. A printhead according to claim 1, wherein themanifold is substantially semi-circular.
 9. A printhead according toclaim 8, wherein the outlet(s) from the manifold are located on thesubstantially straight boundary of the manifold.
 10. A printheadaccording to claim 1, wherein the manifold is a substantially ellipticalor parabolic chamber.